Inkjet printing is a well-known technique for printing or marking information (e.g., manufacturing and/or expiration dates, lot numbers, manufacturing locations, etc.) or images on packages of consumer products such as dairy products, beverages, snacks, food products, plastic bottles, PVC pipes, electrical wirings, etc. Such markings provide manufacturers with useful information for tracking products from their production lines to retail locations where they are being sold to consumers. Product traceability is an important issue in protecting public health and managing supply chain because it allows a manufacturer or public agency to quickly and accurately identify any contaminated goods, and then remove them from the marketplace.
In recent years, the spread of counterfeit goods and the number of infringing goods increase significantly. Reselling of spoiled or lost inventory and contaminated products also happens frequently, thus threatening public health. One of the causes of these issues is attributed to the fact that current markings on packaging printed by inkjet printing technology are not permanent. The marks can be easily removed by either physical or chemical methods. In fact, this is a well-known and a long standing problem to the industries for products with markings on plastic surfaces. Therefore, in order to protect the product information and provide product traceability, there is an urgent need to develop printing systems that are capable of printing irremovable or indelible markings on plastic-based packaging materials.
To tackle the counterfeit issue, a range of anti-counterfeit technologies have been developed up to now. For pharmaceutical industries, well-known and widely used anti-counterfeit technologies include holograms and radio-frequency identification (RFID). However, holograms techniques can be easily reproduced and counterfeited. Nowadays, the RFID technologies are regarded as the most promising technologies for trace and track of the pallets and packages. The sophisticated RFID system allows tracing and securing the pharmaceutical supply chain. However, RFID still cannot prevent package tampering and intelligent hacking. Furthermore, RFID technologies are very expensive to be applied to those fast moving consumer goods (FMCG) such as dairy products, beverages, and food products. Therefore, there is a great demand for an affordable and reliable anti-counterfeiting technique for FMCG packaging.
In last decade, indelible inkjet ink formulations have been scarcely developed and used in printing codes or markings of industrial products from high speed production line with the “continuous inkjet” (CIJ) printing technology. For example, U.S. Pat. No. 5,449,400 has disclosed an anti-counterfeiting ink composition for invalidating bank notes or similar valuables by staining them permanently.
U.S. Pat. No. 5,847,024 has described an anti-counterfeiting non-yellowing watermark ink on papers.
U.S. Pat. No. 7,297,201 has described an inkjet ink composition that forms indelible images on porous or semi-porous substrate such as paper or postage stamps. The inkjet ink composition comprises (i) a hydrophobic colorant carrier, (ii) a first colorant that is soluble in the carrier; (iii) a second colorant comprising a pigment, which is dispersed in the carrier. The solubility difference between different colorants makes the resulting marks highly resistance against any chemical attacks.
U.S. Pat. No. 7,081,158 has disclosed an ink formulation containing more than 70% by weight of propylene carbonate as a solvent. The ink formulation has a high penetration capacity on paper substrates such as letters and postal articles. Propylene carbonate functions as a penetrant to carry the dyes passing through the substrate into inner layer of the substrate. The substrate then serves as a barrier to endow the penetrated dyes with good resistance to any physical and chemical stress.
U.S. Pat. No. 7,833,334 has disclosed an improved propylene carbonate-based ink formulation based on the U.S. Pat. No. 7,081,158. The formulation renders its good adhesion ability and extends its application to various substrates, such as, metal, plastics, glass, etc.
To address the moisture sensitive issue of the propylene carbonate-based ink, U.S. Pat. No. 8,282,724 has disclosed a water-free ink composition, wherein the inkjet ink composition contains organic compounds that are capable of dissociating the ionizable species. The presence of these ionizable species overcomes the problem of low ink conductivity arising from the absence of water for dissolving the conductive salt.
All of the inkjet ink compositions disclosed by the above patent references are mainly for printing indelible or anti-counterfeit markings on paper and postage stamps. They are not for printing indelible or anti-counterfeit markings on nonporous polymer substrates, such as low density poly(ethylene), high density poly(ethylene), poly(phenyl ether), polyolefin, poly(propylene), ethylene-vinyl acetate copolymers, epoxy resins, and the like. As mentioned earlier, the marks produced by the current inkjet ink can be easily removed by either physical or chemical methods.
It is one of the objectives of the present invention to overcome the disadvantages and problems mentioned above.